How is electricity measured and used?
In this unit students explore the ways that current electricity is used and measured in common household devices. To accomplish this they try to light a bulb using a hand generator and wires. Then students investigate the effects of changing the speed and direction of cranking the generator or reversing the connections of the wires. Next, a strand of steel wool is substituted for the bulb and students compare the effects of varying amounts of electrical current from the generator on these two loads. This leads to the development of a circuit concept that consists of an electrical source, connecting conductors (wires), and a load or electrical device. Students investigate simple series and parallel circuits using multiple batteries and loads, such as bulbs, and begin to differentiate between current flow, voltage, and resistance in such circuits. This can be complemented by having students use an online circuit construction simulator such as the PheT Circuit Construction Kit (available online). These concepts are also connected to the language used in electrical measurements, volts, amps, and ohms. Further investigations lead to Ohm’s Law that describes the relationship between these electrical quantities. Students develop the idea of a circuit diagram and simple symbols as a way to represent and analyze circuits. The role of switches, short circuits, fuses, circuit breakers, and their placement in a circuit is then introduced. They investigate the concept of electrical power and the meaning of watts as a unit of power. This leads to the development of the idea of the flow of electrical energy and its transformation to other forms of energy in various appliances. Specifically, students investigate the different factors that effect the changes in water temperature when an electrical heating coil is used to heat water. This leads to further investigations of the typical energy usages by home electrical appliances and the analysis of how the electric power company determines one’s electric bill.
P3.1c Provide examples that illustrate the importance of the electric force in everyday life.
P3.7x Electric Charges — Interactions
P3.7g Propose a mechanism based on electric forces to explain current flow in an electric circuit.
P4.2 Energy Transformation
P4.2A Account for and represent energy transfer and transformation in complex processes (interactions).
P4.2B Name devices that transform specific types of energy into other types (e.g., a device that transforms electricity into motion).
P4.2C Explain how energy is conserved in common systems (e.g., light incident on a transparent material, light incident on a leaf, mechanical energy in a collision).
P4.3 Kinetic and Potential Energy
P4.3A Identify the form of energy in given situations (e.g., moving objects, stretched springs, rocks on cliffs, energy in food).
P4.10 Current Electricity — Circuits
P4.10A Describe the energy transformations when electrical energy is produced and transferred to homes and businesses.
P4.10B Identify common household devices that transform electrical energy to other forms of energy, and describe the type of energy transformation.
P4.10C Given diagrams of many different possible connections of electric circuit elements, identify complete circuits, open circuits, and short circuits and explain the reasons for the classification.
P4.10D Discriminate between voltage, resistance, and current as they apply to an electric circuit.
P4.10x Current Electricity — Ohm’s Law, Work, and Power
P4.10e Explain energy transfer in a circuit, using an electrical charge model.
P4.10g Compare the currents, voltages, and power in parallel and series circuits.
P4.10h Explain how circuit breakers and fuses protect household appliances.
P4.10i Compare the energy used in one day by common household appliances (e.g., refrigerator, lamps, hair dryer, toaster, televisions, music players).
P4.10j Explain the difference between electric power and electric energy as used in bills from an electric company.
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- What is electricity?
- What types of energy transformations take place in common electrical devices such as bulbs, motors, and heaters?
- In what ways can multiple devices be connected to an electrical source in a circuit?
- How are electrical circuits described and used?
- What roles do switches, fuses, circuit breakers, and electrical shorts play in electrical circuits?
- What are the relationships between current, voltage, resistance, and power in a circuit?
electrical power (P = IV)
moving electric charge
Ohm’s Law (V = IR)
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